The present invention relates to an apparatus for measuring the relative speed, direction and temperature of air moving past an ultrasonic sensing probe. In particular, the present invention comprises a wind vector, velocity and temperature measuring apparatus utilizing variations in the propagation time of ultrasonic waves moving from a transmitting transducer means to a plurality of spatially positioned receiving transducer elements.
An aircraft in flight is normally moving so that air will be flowing past the aircraft or moving relative to the aircraft. In order to exercise optimum control over the aircraft itself, or over operations associated with the aircraft when in flight, it is necessary to know the manner in which air is moving past the aircraft. By having an accurate measure of the air movement and its temperature, it is then possible to obtain a measure of the forces that are being exerted on the aircraft.
The air movement relative to the aircraft is most conveniently considered in three dimensions; related to the aircraft itself, the directions being along a primary or forward and reverse axis of the aircraft, a vertical axis extending up and down at a right angle to the primary axis of the aircraft, and a horizontal axis extending left and right at a right angle to the primary axis of the aircraft.
Ultrasonic measuring devices have been utilized heretofor for purposes of measuring liquid and gaseous flows. In addition, ultrasonic anemometers and temperature sensors have been built but such apparatus heretofore known has not been suitable or practical for use in aircraft installations where factors of size, weight and accuracy must be optimized.
Representative ultrasonic anemometer type apparatus heretofore known will be found in the following identified references:
"A Continuous-Wave Sonic Anemometer-Thermometer", J. C. Kaimal and J. A. Businger (manuscript received Mar. 5, 1962) (pp. 156-167) PA1 "Deriving Power Spectra from a Three-Component Sonic Anemometer", J. C. Kaimal, J. C. Wyngaard and D. A. Haugen, October, 1968. (pp. 827-837) PA1 "Improvements and Refinements on a Pulse Type Sonic Anemometer", Arthur Bisberg, Arthur Papas, and David J. Beaubien. (pp 1-50) PA1 "Wind Speeds as Measured by Cup and Sonic Anemometers and Influenced by Tower Structure", Yutaka Izumi and Morton L. Barad, December, 1970. (pp. 851-856)
In a copending application of D. J. Rotier entitled "Air Movement Measuring Apparatus", Ser. No. 675,036, filed Mar. 8, 1976, there is disclosed a three element ultrasonic probe for an aircraft that is intended for measuring relative air movement vector and velocity. As the movement of an ultrasonic signal through air is a function of the temperature of the air, it is necessary to know the air temperature in determining relative airspeed. The probe in the aforesaid application makes use of a platinum wire temperature sensor to provide a temperature signal needed to compensate for the ultrasonic signal propagation time changes caused by variations in temperature. Such an arrangement is relatively expensive and does not provide the accuracy required for some applications where a substantially instantaneous measure of air temperature is required.